Plasma pharmacokinetics of the indenoisoquinoline topoisomerase I inhibitor, NSC 743400, in rats and dogs.

PURPOSE: NSC 743400 is a novel synthetic indenoisoquinoline analog under development as an anticancer agent. It is a potent topoisomerase I inhibitor with potential therapeutic advantages over FDA-approved camptothecin derivatives. In preparation for clinical development of NSC 743400, we determined the pharmacokinetics after administration to rats and dogs. METHODS: NSC 743400 was administered intravenously at a dose of 12 or 24 mg/m(2) to rats (single bolus) or 10, 50, 100, 215, 430, or 646 mg/m(2) (intravenous infusion) or 860 or 1720 mg/m(2) (orally) to dogs. RESULTS: Intravenously administered NSC 743400 was eliminated from both species with an estimated t 1/2 of 2-5 h in rat and 6-14 h in dog. Elimination t 1/2 increased with dose in dog. Area under the plasma concentration-versus-time curve (AUC) was comparable in both species, at about 300-400 h ng/mL for the approximately 10 mg/m(2) dose groups. Overall, AUC values increased proportionally with dose for both species but had evidence of more than proportional exposure at the highest doses. Oral dosing resulted in variable drug absorption. CONCLUSIONS: The pharmacokinetic data were used to plan first-in-human clinical trials.

Plasma pharmacokinetics and oral bioavailability of the 3,4,5,6-tetrahydrouridine (THU) prodrug, triacetyl-THU (taTHU), in mice.

PURPOSE: Cytidine drugs, such as gemcitabine, undergo rapid catabolism and inactivation by cytidine deaminase (CD). 3,4,5,6-tetrahydrouridine (THU), a potent CD inhibitor, has been applied preclinically and clinically as a modulator of cytidine analogue metabolism. However, THU is only 20% orally bioavailable, which limits its preclinical evaluation and clinical use. Therefore, we characterized THU pharmacokinetics after the administration to mice of the more lipophilic pro-drug triacetyl-THU (taTHU). METHODS: Mice were dosed with 150 mg/kg taTHU i.v. or p.o. Plasma and urine THU concentrations were quantitated with a validated LC-MS/MS assay. Plasma and urine pharmacokinetic parameters were calculated non-compartmentally and compartmentally. RESULTS: taTHU did not inhibit CD. THU, after 150 mg/kg taTHU i.v., had a 235-min terminal half-life and produced plasma THU concentrations >1 µg/mL, the concentration shown to inhibit CD, for 10 h. Renal excretion accounted for 40-55% of the i.v. taTHU dose, 6-12% of the p.o. taTHU dose. A two-compartment model of taTHU generating THU fitted the i.v. taTHU data best. taTHU, at 150 mg/kg p.o., produced a concentration versus time profile with a plateau of approximately 10 µg/mL from 0.5-2 h, followed by a decline with a 122-min half-life. Approximately 68% of i.v. taTHU is converted to THU. Approximately 30% of p.o. taTHU reaches the systemic circulation as THU. CONCLUSIONS: The availability of THU after p.o. taTHU is 30%, when compared to the 20% achieved with p.o. THU. These data will support the clinical studies of taTHU.

Liquid chromatography-tandem mass spectrometric assay for the quantitation in human plasma of the novel indenoisoquinoline topoisomerase I inhibitors, NSC 743400 and NSC 725776.

Topoisomerase I (Topo I) is a recognized target for ovarian, lung, and colorectal cancer therapy. The FDA-approved camptothecin (CPT) Topo I inhibitors, topotecan and irinotecan are labile and their effects are rapidly reversible. The indenoisoquinoline topoisomerase I inhibitors, NSC 743400 and NSC 725776, have been developed as a new generation of Topo I inhibitors and are being advanced to clinical evaluation. To support the clinical development of NSC 743400 and NSC 725776, we developed and validated, according to FDA guidelines, LC-MS/MS assays for the sensitive, accurate and precise quantitation of NSC 743400 and NSC 725776 in 0.2 mL human plasma. After ethyl acetate extraction, separation was achieved with a Synergi Polar RP column and a gradient of 0.1% formic acid in acetonitrile:water. NSC 743400 and NSC 725776 eluted at approximately 3 min, and the total run time was 14 min. Detection consisted of electrospray, positive-mode ionization mass spectrometry. Between 3 and 1000 ng/mL, accuracy was 96.9-108.2% for NSC 743400 and 95.1-106.7% for NSC 725776, and precision was <11.4% for NSC 743400 and <5.9% for NSC 725776. Extraction recovery was >80% for both analytes, and ion suppression ranged from -46.7 to 5.7%. The use of isotopically labeled internal standards and a wash phase at the end of the run were necessary to achieve adequate assay performance. Protein binding in human plasma as assessed by equilibrium dialysis showed both indenoisoquinolines to be more than 98% protein bound.